Gene product distribution is often used to infer developmental similarities and differences in animals with evolutionarily diverse body plans. However, to address commonalties of developmental mechanisms, what is really needed is a method to assess and compare gene function in divergent organisms. This requires mutations eliminating gene function. Such mutations are often difficult to obtain, even in organisms amenable to genetic analysis. To address this issue we have investigated the use of double-stranded RNA interference to phenocopy null mutations. We show that RNA interference can be used to phenocopy mutations of the Deformed orthologues in Drosophila and Tribolium. We discuss the possible use of this technique for comparisons of developmental mechanisms in organisms with differing ontogenies.